The invention relates to a magnetic device and a magnetic memory, and in particular, to a magnetic device having recording and reproducing capability and to a magnetic memory using the same.
A conventional method of controlling the magnetization direction of magnetic material is to apply an external magnetic field. For example, in a hard disk drive, a magnetic field generated from a recording head reverses the magnetization direction of the magnetic recording medium to perform write operation. In a solid magnetic memory, electric current generated in a wire placed in the vicinity of a magnetoresistance effect device produces a current-induced magnetic field, which is applied to a cell to control the magnetization direction of the cell. These methods for controlling the magnetization direction with an external magnetic field have a long history and can be viewed as an established technology.
On the other hand, recent advances in nanotechnology have rapidly led to finer magnetic materials. This has created the need for local magnetization control at nanoscale. However, magnetic field is difficult to localize because it basically has the nature of spreading out into space. An attempt to select a bit or cell of a microscopic size for controlling its magnetization direction encounters a “crosstalk” problem of erroneously selecting a nearby bit or cell, or otherwise a great problem that a smaller source for generating magnetic field cannot generate sufficient magnetic field.
More recently, a phenomenon called “current-driven magnetization reversal” was found in which electric current passed directly through a magnetic material causes magnetization reversal (see, for example, F. J. Albert, et al., Appl. Phy. Lett. 77, p3809 (2000)). In this phenomenon, current is spin-polarized by passing through a magnetic layer. This current flow transfers the angular momentum of spin-polarized electrons to the angular momentum of magnetic material subject to magnetization reversal. This phenomenon can be used to act directly on nanoscale magnetic materials. It is thus expected that finer magnetic materials can be used for recording without crosstalk.
However, the “current-driven magnetization reversal” has a problem at present that reversal current for reversing magnetization is extremely high, as much as 10 mA to several mA. A device structure that undergoes magnetization reversal with minimum current is desired in order to prevent device breakdown due to electric current, to prevent heat generation, to reduce power consumption, and to be reasonably combined with a high-resistance layer for detecting magnetoresistance effect for reproducing signals of magnetic tunneling or other effect.
The invention has been made in view of these problems. An object of the invention is to provide a magnetic device that can reduce the reversal current in current-driven magnetic reversal, and a magnetic memory using the same.